The present invention relates to a copy form set which comprises, optionally besides other sheets, a transmitter sheet whose transmitter side is provided with a layer of microencapsulated dye precursors (CB substances), as well as a receiver sheet whose receiver side facing the transmitter side of the transmitter sheet is provided with color-developing adsorbing substances. Further, the invention relates to a transmitter sheet especially for copy form sets of the above kind.
Self-copying papers on the basis of chemical dye reactions (so-called CFR papers) have been known for a long time and are used for various purposes. Form sets of color reaction papers are often composed in that a layer which delivers mostly microencapsulated dye precursors is arranged on the reverse of a transmitter sheet. The delivering layer consists of so-called CB (coated back) substances which contain high-boiling mixtures of solvents, in which various weakly colored dye precursors are solute. On the front side of a receiver sheet disposed below the transmitter sheet there is applied a receiving layer of so-called CF (coated front) substances, which commonly consists of active adsorbents and inorganic and/or organic color developers.
On writing or printing upon such a copy form set the microcapsules of the CB layer are caused to burst in the area which is written or printed upon, so that the CB substances of the transmitter sheet can mix up with the facing CF substances of the receiver sheet. This results in the desired copy face on the receiver side of the receiver sheet.
For most of the applications the copy produced by commercial color reaction paper is sufficient even though it is often relatively weak and without sharp contours. In other applications, which are referred to further in detail hereinafter, an intensified copy is required or desired.